Currently, there are two general types of radial inflow turbines which are utilized in turbochargers. One type is known as a fixed geometry turbine which is configured such that the shape and area of the fluid passage(s), which extends from the fluid inlet to the turbine rotor, can not be physically changed. An example of a fixed geometry turbine is described in U.S. Pat. No. 3,664,761, issued to Zastrow in 1972. The second type of turbine is known as a variable flow turbine, one design of which is configured to have radially positioned inner and outer fluid passages with a valve positioned across one of the passages to regulate the fluid flow therethrough. By regulating the size of the opening to the one passage by moving the valve, one can vary the cross-sectional area of the fluid flow path and thereby compensate for variations in the fluid flow rate and pressure caused by operating an engine at different speeds and loads. An example of a variable flow turbine is described in U.S. Pat. No. 4,177,006, issued to Nancarrow in 1979. In the Nancarrow patent, the turbine has a straight fluid inlet portion which leads into a scroll-shaped portion. Both the fluid inlet portion and the scroll-shaped portion are divided into a pair of flow paths. Each of the flow paths are further divided in the scroll-shaped portion only into primary and secondary flow paths by a wall formed integral with the housing. In addition, a valve is disposed at the fluid inlet across the secondary flow path which may be rotated to direct the flow away from the wall to regulate the fluid flow.
Of the two types of turbines, engines using the fixed geometry turbine are less efficient. This is because in turbocharged engines with a fixed geometry turbine, the turbine is matched to the compressor which is normally configured for maximum efficiency when the engine is at its peak torque. Consequently, the engine cannot operate at optimum efficiency at rated speed and load because the efficient operating flow range of the compressor is less than that required by the engine. A variable flow turbine, on the other hand, can increase the engine's rated point efficiency by using compressors with high efficiency at rated speed and load and lower efficiency when the engine is at peak torque. This is possible because the power of the variable flow turbine can be increased at peak torque to compensate for the lower efficiency of the compressor. Also, engines with variable flow turbines are more efficient at less than maximum speeds and loads where maximum charge air pressure is not needed. In these situations, the variable flow turbines can increase the turbine flow area to reduce the exhaust manifold pressure.
Currently, there is a need to develop a turbocharger with a variable flow turbine which is highly efficient throughout the operating range of the engine. Now, an improved variable flow turbine has been invented which can meet these requirements.